Theoretical and experimental study of a diode-pumped doubly Q-switched Nd:GdVO4 1.34 μm laser with acousto-optic (AO) modulator and V:YAG saturable absorber

A diode-pumped doubly Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm with acousto-optic (AO) modulator and V³⁺:YAG saturable absorber is demonstrated. This doubly Q-switched laser can generate shorter pulse width and higher peak power than the singly Q-switched laser only with an AO modulator or a V³⁺:YAG saturable absorber. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly Q-switched laser at 1.34 μm under Gaussian approximation are given. The numerical solutions of the equations are in agreement with the experimental results.     

Efficient diode-pumped passively Q-switched laser with Nd:YAG/Cr:YAG composite crystal

Diffusion bonded Nd:YAG/Cr:YAG composite laser crystal has been employed to perform a compact diode-pumped passively Q-switched laser. At the incident pump power of 3.3 W and pulse repetition rate of 16.3 kHz, the maximum average output of 592 mW has been obtained, corresponding to an optical-to-optical conversion efficiency of 18%. Stable passively Q-switched operation with peak power of 6.5 kW and pulse duration of 6 ns was also achieved. It has been experimentally revealed that Nd:host/Cr:YAG composite structure is a promising material for compact cost-effective Q-switched laser sources with high-peak power and short pulse duration. In addition, thermal lens effect (TLE) in the active medium and its impact on the Q-switched laser performance have been analyzed.     

Improved performance of acoustooptically Q-switched Nd:GdVO<Subscript>4</Subscript> laser by using the planoconvex cavity

A planoconvex cavity is used to compensate the thermal lens effectively for a Q-switched Nd:GdVO₄ laser. The good beam quality of the continuous-wave (CW) output laser was obtained and the performances of the Q-switched laser were improved remarkably. The pulse width reduced and the output ratio of the Q-switching to free running increased resulting from the good beam quality of the planoconvex cavity compared with those used on a flat-flat cavity.     

High power CW and Q-switched operation of a diode-side-pumped Nd: YAG 1319-nm laser

We demonstrated the highly efficient continuous wave(CW)and Q-switched infrared laser from a diodeside-pumped Nd:YAG crystal.A CW output as high as 66 W at 1319 nm was achieved under the pump power of 460 W,corresponding to a coversion efficiency of 14.3%.A maximum average power of 8.9 W of TEM00 mode was obtained in Q-switched operation at the repetition rate of 8 kHz.The performance of the laser considering the thermal lens effect induced by pump power Was also analyzed.     

Experimental analysis of a continuously pumped,repetitively Q-switched Nd/YAG laser

The threshold operation and performance of a high pulse repetition frequency Nd/YAG laser are discussed. A rotating mirror Q-switch was used, and detailed studies of the variation of Q-switched threshold with motor frequency, and of the pulse build-up time with input power have been carried out. The results indicate that the switching angle varies with mirror reflectivity but is practically independent of resonator length. The latter is attributed to thermal lens action in the laser rod modifying the nominally plane parallel resonator configuration thereby leading to a spherical configuration. Under these conditions, the switching angle becomes independent of resonator length, but depends strongly on the induced focal length of the lens (laser rod). The degrading effect on the Q-switched laser performance of the mis-match at the laser rod surfaces is then discussed and finally the conditions for achieving maximum energy output in a single pulse are derived and experimentally verified.     

A stable 10 kHz–1.3 MHz high repetition rate continuously controllable AO Q-switched Nd:YVO4 laser

A stable AO Q-switched Nd:YVO₄ laser using diode-end-pumped structure is presented. By optimizing laser crystal, pumping laser and controlling electric parameters to eliminate thermal lens difference, this AO Q-switched laser can reach 1.3 MHz repetition rate and achieve stable pulse in large range from 10 kHz continuously to 1.3 MHz. The important relationship between repetition rate and electric parameters, including pumping current, duty cycle of electric pulse, are also presented. Output average power and pulse width at 1.3 MHz are 4 W and 35 ns, respectively.     

High stability of electro-optically Q-switched Ce:Nd:YAG laser by using the optimized concavo-convex cavity

In order to solve the hard problem of laser instability, an electro-optically Q-switched Ce:Nd:YAG laser by using the optimized concavo-convex cavity is demonstrated. The laser with the optimized cavity is insensitive to the thermal lens of laser crystal and has excellent stability of average output pulse energy and threshold voltage under different environment temperature of −45, 25, and 55°C.     

High-energy Q-switched operation of a fiber-laser-pumped Er:YAG laser

A high-energy Q-switched Er:YAG laser in-band pumped by an Er,Yb co-doped fiber laser is reported. A simple two-mirror multi-mode resonator incorporating an electro-optic Q-switch and a multi-Brewster-plate polarizer was employed, together with a simple compensation scheme to reduce the depolarization loss due to thermally induced stress birefringence in the Er:YAG crystal at high pump powers. The laser yielded Q-switched pulses at 1617 nm with 30.5-mJ pulse energy and <20-ns pulse duration (FWHM) at 20-Hz repetition rate, corresponding to a peak power of >1.5 MW for 55 W of pump power at 1532 nm. The prospects for further improvement in Q-switched performance are discussed.     

Greatly improved stability of passively Q-switched Ce:Nd:YAG laser by using corner cube prism

In order to solve the hard problem of laser instability, a miniature Cr⁴⁺:YAG Q-switched Ce:Nd:YAG laser with a retroreflecting corner cube prism is demonstrated. The corner cube prism is insensitive to misalignment in any direction. Laser cavity with the prism is found to meet the condition of violent change of environment temperature and the variation of thermal lens of laser crystal by our experiment. Compared with flat-flat cavity, stability of the laser with a retroreflecting corner cube prism is improved remarkably.     

Diode-pumped passively Q-Switched intracavity OPO with a folded cavity configuration

We present in this report an efficient KTP-based intracavity optical parametric oscillator driven by a diode-pumped Nd:GdVO₄/Cr:YAG passively Q-switched laser. For the first time, a novel folded cavity configuration was employed to set the KTP and Cr:YAG crystals separately at different fundamental beam waists. Based on the ABCD-matrix theory and by taking the thermal lens effect into account, the laser cavity was well optimized to enhance the OPO performance. A diode pump threshold as low as 1.2 W and a maximum signal (1.57 μm) average output power up to 560 mW have been achieved. Efficient energy transfer in the IOPO leads to short pulse duration (1.8–2.6 ns) and high peak power (6.8 kW) output at 1.57 μm. Additionally, the correlation dynamics between the pump laser and the OPO was analyzed in detail.     

Excellent stability of laser passively Q-switched with a retroreflecting corner cube prism

A miniature Cr⁴⁺:YAG Q-switched, repetitive operation, conductive cooling Nd:YAG laser with a retroreflecting corner cube prism is demonstrated. The corner cube prism which is insensitive to misalignment in any direction makes it useful for the laser to adapt to the violent change of ambient temperature and also makes the laser cavity insensitive to the variation of thermal lens of the crystal. The laser has excellent stability of the average output pulse energy and the threshold voltage under different ambient temperature of −40, 25, and 55°C.     

Dual-polarization electro-optical Q-switched ceramic laser

A dual-polarization electro-optical Q-switched Nd:YAG ceramic laser was studied. By selecting the appropriate size of calcite crystals, the dual-polarization Q-switched pulse was achieved by characteristics of calcite crystal. Experimental results show that compared with the traditional single-polarization electro-optical Q-switched laser, insertion loss is reduced, dynamic to static ratio is greatly improved, thermally induced birefringence of electro-optical Q-switched Nd:YAG ceramic laser is effective compensated. The output power of 19 W and the pulse width of 13 ns are obtained at the repetition rate of 1 kHz and pumped power of 144 W. The dynamic to static ratio is 71%. The results formed the basis for the further development of the high power and high efficiency ceramic red laser.     

Diode end pumped Nd:YAG laser at 946 nm with high pulse energy limited by thermal lensing

Diode lasers with peak powers in the kW range and pulse durations of micro- to milli-seconds have been available since several years. Pumping solid state lasers with such sources yield high output pulse energies in spiking or Q-switched operation. The output energy is limited by the thermal lens effects, which are measured and calculated. The time dependent heat conduction equation in the laser crystal is solved numerically to predict the overall temperature rise and thermal lensing. The thermally induced optical path difference is approximated by a quadratic distribution to obtain the focal length f of the thermal lens. The thermal lens coefficient K=1/(f⋅P _av), which depends only weakly on the heat transfer coefficient H of the laser crystal to the heat sink, decreases exponentially with increasing pump frequency until the steady state is reached. Experiments were done with a Nd:YAG crystal at different pump frequencies up to 100 Hz. The thermal lens coefficients obtained by the power maxima of asymmetric flat-flat resonators agree with our calculations.     

High energy and high stability Cr:YAG passively Q-switched laser with convex-ARR unstable resonator

A convex-ARR (Anti-resonant Ring) unstable resonator was introduced in a Cr⁴⁺:YAG passively Q-switched Nd:YAG pulsed laser. There are two novel features in this cavity, one is the unstable resonator increasing output energy and improving laser mode; the other is the ARR structure efficiently enhancing the laser stability. A high energy and high stability Q-switched pulse with a single pulse energy of 85.6 mJ, a pulse width of 38 ns and an energy stability of 99.6% was obtained. The experimental results were analyzed well by using the mechanism of transient grating and the properties of the unstable resonator.     

Performance of 2 μm Tm:YAP pulse laser based on a carbon nanotube absorber

We demonstrated the first use of carbon nanotube as a saturable absorber in the Q-switched and Q-switched mode-locking of a diode pumped Tm:YAP operating at 2 μm. At the incident pump power of 8.64 W, the minimum Q-switched pulse width of 255.1 ns, and the maximum peak power 53.1 W can be obtained with the corresponding repetition rate of 21.76 kHz. The performance of a diode-pumped passively Q-switched mode-locked Tm:YAP laser with high repetition rate formed with a folded cavity. As high as 780 mW average output power was produced in QML laser. The repetition rate of the mode-locked pulse inside the Q-switched envelope was 244.1 MHz. The dependence of the operational parameters on the pump power was also investigated experimentally.     

A study of a Q-switched double-clad ytterbium-doped fiber laser with amplifying effect

A high repetition rate ytterbium-doped double-clad (YDDC) fiber laser with amplifying effect is described by using acousto-optic modulator. The characteristic of Q-switched pulses are studied with accurate control of opening gate time of modulator. The stable Q-switched pulses with tens of nanoseconds width can be observed at high repetition rate varied from 50 kHz to 500 kHz using this laser. The stable operation area of the Q-switched fiber laser is discussed and the analysis results agree well with that of the experiment.     

Operation of a Raman laser in bulk silicon

A Raman laser based on a bulk silicon single crystal with 1.127 μm emission wavelength is demonstrated. The Si crystal with 30 mm length was placed into an external cavity and pumped by a Q-switched Nd:YAG master oscillator power amplifier system. Strong defocusing of the pump and Raman laser beam by free carriers was compensated by an intracavity lens. Raman laser operation with a pulse duration of 2.5 ns was identified by a Raman laser threshold significantly lower than the single-pass stimulated Raman-scattering threshold. Linear absorption losses of the 1.06415 μm pump radiation are strongly reduced by cooling the Si crystal to a temperature of 10 K.     

High-power non-astigmatic TEM<Subscript>00</Subscript> and vortex mode generation in a compact bounce laser design

A novel design of a diode-side-pumped bounce amplifier laser is described that can produce a high-power TEM₀₀ mode and Laguerre–Gaussian (LG) vortex mode operation with high circularity and low astigmatism. The design utilises control of pump size and bounce angle such that the laser mode experiences substantially circular symmetric gain and spherical thermal lensing, in a highly compact fundamental mode resonator. In a simple plane–plane Nd:YVO₄ laser resonator with no other optical components and total length of just 13.4 cm, highly circularised TEM₀₀ operation is produced at wavelength 1064 nm, with 14.2 W of power and high beam quality M ²<1.05. Stable Q-switched TEM₀₀ operation is demonstrated up to 900 kHz and second harmonic power of 7.2 W at 532 nm is generated with conversion efficiency up to 64%. Minor modification of the design to exploit the spherical aberration of the thermal lens is shown to allow for generation of a doughnut-shaped LG vortex mode with average power 16.6 W, maintaining extremely low astigmatism. Q-switched operation of the vortex mode is accomplished up to 400 kHz. A detailed numerical thermal analysis of the amplifier design is performed and gives quantitative agreement with experimental results.     

Compact and efficient Kerr-lens mode-locked diode-pumped actively Q-switched YVO4-Nd:YVO4 laser

By using a simple linear configuration, a stable and efficient YVO₄-Nd:YVO₄ laser, actively Q-switched by an acousto-optic modulator and passively mode-locked by KLM is realized, from which the great average output power, the high efficiency are obtained and the mode-locked pulse inside the Q-switched pulse has a repetition rate of 470 MHz. The nearly 100% modulation depth of the Q-switched mode-locked pulses can be obtained at any pump power over the threshold. Considering the Kerr-lens effect of laser medium and Q-switching by an acousto-optic modulator, we have analyzed the self-mode-locked YVO₄-Nd:YVO₄ laser by using the nonlinear ABCD propagation matrix and the hyperbolic fluctuation mechanism. The numerical solutions are in good agreement with the experimental results.     

多波长半导体激光阵列端泵Nd:YAG脉冲激光器

研制了无温控多波长激光二极管阵列端面泵浦Nd：YAG电光调Q激光器。采用4 000 W多波长准连续激光二极管阵列作为泵浦源,快轴准直镜与透镜导管作为泵浦耦合系统,端面泵浦φ6 mm×60 mm的Nd：YAG晶体,并采用RTP晶体进行电光调Q实验。在重复频率5 Hz、室温（25℃）时,激光器获得了最大输出能量74.4 mJ、脉宽15 ns的1 064 nm脉冲激光输出,光光转换效率达到11%。在25~55℃的工作温度下,对多波长LDA的光谱特征与激光器的输出特性作了测试,激光器输出能量随着工作温度的上升而先迅速下降再逐步保持稳定,当重复频率分别为5 Hz和10 Hz时,激光器对应的最低输出能量分别为48 mJ与37 mJ。